The invention relates to a valve for metering a fluid, provided with a housing with at least one metering opening and at least one closing member which is movable between a position closing the opening and a position leaving the opening at least partially clear, which closing member is biased by biasing means co-acting therewith to one of its positions and can be placed in the other position counter to the bias by operating means. Such a metering valve is known and is used for instance in fuel injection systems, particularly systems for injecting gaseous fuel, such as the LPG injection system marketed by Autogastechniek Holland B.V. under the name DGI.
Current metering valves or vapour injectors are provided with a closing member or plunger which is pulled from the seat by an electromagnet counter to the force of a mechanical spring and which is pressed by the spring back onto the seat after the electromagnetic force has been removed. Because the plunger must be opened counter to a spring force, the force required of the electromagnet is greater than should actually be necessary. Both the electromagnetic coil and the plunger must hereby be embodied disproportionately larger and heavier than would be necessary in the absence of the spring.
The unnecessarily heavy plunger causes problems in respect of the so-called rebounce, i.e. the rebound which occurs when the heavy plunger strikes at great speed against the upper stop at the end of the attractive phase of the electromagnet. This phenomenon of rebounce results in a non-linear and unstable metering behaviour, which is furthermore temperature and injector-dependent. As a result it is not easily possible to produce this type of vapour injector in large numbers with sufficient precision.
In the DGI system mentioned above, this problem is solved by using a control of the vapour injector with feedback, whereby variations in the metering behaviour as a result of rebounce are measured and can be corrected by feedback. However, this system is relatively expensive and therefore particularly suitable for group injection or monopoint injection, wherein a single central injector is present for metering of the gas, which is then guided alternately to the desired cylinders via a nozzle.
The invention therefore has for its object to provide an improved metering valve which is simpler, smaller and lighter than the known valve and which can thus be manufactured at lower cost. Such a valve would then be suitable for application in a system of individual injection per cylinder, or a multipoint injection system.
According to the invention this is achieved in that the biasing means comprise at least one pneumatic or hydraulic spring.
Owing to the pneumatic (or hydraulic) closing of the valve, preferably a diaphragm, optionally in combination with the electromagnetic opening thereof, the use of spring force becomes unnecessary. The coil and the plunger can hereby take a small and light form such that the problem of rebounce no longer occurs. The pneumatic or hydraulic spring is preferably operated by the fluid for metering. By using the fluid itself to operate the valve a simple and robust construction is obtained with relatively few components.
The operating means can advantageously be of electromagnetic type, whereby a simple control is possible. The operating means can herein then comprise a coil with U-shaped armature and at least one metal attraction element connected to the closing member. This attraction element is preferably plate-like. Thus, as a result of the chosen embodiment with the U-shaped armature and flat plunger plate, a relatively small electromagnetic force is required, so that a so-called high-impedance coil can suffice. This has the further consequence that the electrical control can be provided using a simple low side driver, such as is also known from modern petrol injection systems. If the metering behaviour of the valve were made the same as that of a petrol injector, it would even be possible to control the valve directly from the engine management computer of the petrol engine.
The closing member is preferably formed by a diaphragm. Such a diaphragm is light and of simple construction and can be operated with little force. The diaphragm then advantageously has a relatively stiff central portion co-acting with the opening for closing, and a relatively flexible edge portion. A good sealing and yet easy deformability of the diaphragm are thus obtained simultaneously.
The closing member can be accommodated in a housing which has on either side of the closing member at least one supply opening connected to a feed conduit for the fluid for metering. The closing member can thus be operated by admitting fluid on either side thereof. The supply openings are preferably dimensioned herein such that the fluid pressure in the housing on the side of the closing member directed toward the opening for closing is lower than the pressure on the opposite side thereof.
The invention further also relates to a system for supplying fuel to a combustion engine, provided with a container for the fuel and at least one feed line connecting the container to the engine, in which line is received at least one metering valve of the above described type. The engine herein preferably has a number of combustion chambers and at least one metering valve is present for each combustion chamber. A precisely operating multipoint injection system is thus obtained which can be manufactured in simple manner and at low cost.